Tank vessels are designed to carry liquefied loads or gases on roads, seas, oceans, and rails. Many variants exist due to the wide variety of liquids and gases that can be transported. The tank vessels, for many long-distance transportation uses, tend to be large and may be insulated, pressurized, and designed for single or multiple loads (often by means of internal divisions in their tank). A tank vessel may have several openings and valves to monitor, protect against, and release pressure buildup within the tank vessel. A tank vessel may be loaded through a manway on a top part of the tank vessel, and unloaded through an opening in the bottom of the tank vessel. In some instances, the tank vessel may be loaded with a liquid material (e.g., paraffin, rosins, resins, etc.) that solidifies at typical atmospheric ambient temperatures. In these instances, the tank vessel may be insulated to maintain the higher temperature of the material and thus enable faster unloading without extra time spent melting the liquid material.
During transportation of the material from within the tank vessel, the pressure within the tank vessel may increase. To protect against this potential pressure buildup, precautionary measures may include opening a relief valve at the top of the tank vessel to allow gas (e.g., air) to exit the tank vessel to maintain the pressure. These relief valves are often in thermal contact with the exterior of the tank vessel and, thus, generally have a temperature that is the atmospheric ambient temperature. For materials that are solid at atmospheric ambient temperature, the relief valves may be plugged as the liquid material is agitated during transport. The transported material washes over the relief valve, which repeatedly applies a thin layer to the interior of the relief valve. That is, as the tank vessel shifts during transport, the material may slosh over the relief valve, leaving a small amount of the material. After many hundreds of applications of the material, a significant plug may develop.
The plugs that develop within the tank vessel may also be detrimental during evacuation of the material. In many instances, the material exits the tank vessel through an opening in the bottom, taking advantage of the pull due to gravity. To allow the material to better flow out, a manway or other opening may be opened in the top of the tank vessel, enabling pressure to equalize from the top while material exits the bottom. The plugs may block this pressure equalization, slowing the material, or causing damage to the tank vessel.
Removing such plugs may be a difficult and/or time consuming project for an operator. The operator may climb up a ladder to the top of the tank vessel and open the valve by twisting nuts or bolts, which in many cases can be pressurized due to the plugs on the relief valves. Indeed, due to the plugs developed on the valves, the operator may be unaware of the dangerous condition since any reading of the internal pressure of the tank vessel may be unreliable. A pressurized tank vessel may result, in some instances, in an operator being injured by the valve itself, or by sudden shifting of the valve causing the operator to fall from the tank vessel.
A need exists for a release valve that reliably remains free from plugs caused by solidifying material on an interior surface of the release valve. The embodiments described below address this need.
A need exists for a release valve that may be opened from a ground surface near a tank vessel without requiring an operator to climb to the top of the tank vessel. The embodiments described below address this need.